Where’s the rest of the question? Am I supposed to solve this completely?
10 different pairs. Since there are 5 different brands you simply add 4+3+2+1 to get 10.
x
---- = 5 (solve for x)
0.6
x = 5(0.6)
x = 3
then....
3
----- = 15
0.2
your answer should be 15 ft per second.
hope this helps :)

Solution:
Given data:
and 
To find
:

Distributive property: 



Arrange and add/subtract same powers.


Hence 